Split AbstractXApplication mainLoopIteration

Linked: #577

src/Magnum/Platform/AbstractXApplication.cpp

@@ -139,11 +139,7 @@ int AbstractXApplication::exec() {
     return _exitCode;
 }
 
-bool AbstractXApplication::mainLoopIteration() {
+bool AbstractXApplication::mainLoopEventIteration() {
-    /* If exit was requested directly in the constructor, exit immediately
-       without calling anything else */
-    if(_flags & Flag::Exit) return false;
-
     XEvent event;
 
     /* Closed window */
@@ -184,11 +180,29 @@ bool AbstractXApplication::mainLoopIteration() {
             } break;
         }
     }
+}
 
+bool AbstractXApplication::mainLoopDrawEventIteration() {
     if(_flags & Flag::Redraw) {
         _flags &= ~Flag::Redraw;
         drawEvent();
-    } else Utility::System::sleep(5);
+        return true;
+    }
+    return false;  
+}
+
+bool AbstractXApplication::mainLoopIteration() {
+    /* If exit was requested directly in the constructor, exit immediately
+       without calling anything else */
+    if(_flags & Flag::Exit) return false;
+
+    /* exit was requested in the event loop */
+    if (!mainLoopEventIteration())
+        return false;
+
+    /* If not drawing anything, delay to prevent CPU hogging */
+    if (!mainLoopDraweventIteration())
+        Utility::System::sleep(5);
 
     return !(_flags & Flag::Exit);
 }

src/Magnum/Platform/AbstractXApplication.h

@@ -134,14 +134,34 @@ class AbstractXApplication {
          *      should exit, @cpp true @ce otherwise
          * @m_since{2020,06}
          *
+         * Calls @ref mainLoopEventIteration() and @ref mainLoopDrawEventIteration()
+         * managing the delays between them.
          * Called internally from @ref exec(). If you want to have better
          * control over how the main loop behaves, you can call this function
+         * (or the sub mainLoopIteration functions)
          * yourself from your own `main()` function instead of it being called
          * automatically from @ref exec() / @ref MAGNUM_GLXAPPLICATION_MAIN()
          * / @ref MAGNUM_XEGLAPPLICATION_MAIN().
          */
         bool mainLoopIteration();
 
+        /**
+         * @brief Process pending application events
+         * @return @cpp false @ce if @ref exit() was called and the application
+         *      should exit, @cpp true @ce otherwise
+         * 
+         * Called internally from @ref mainLoopIteration().
+         */
+        bool mainLoopEventIteration();
+
+        /**
+         * @brief Calls @ref drawEvent() if @ref Flag::Redraw is set and unset it.
+         * @return @cpp true @ce if @ref drawEvent() was called, @cpp false @ce otherwise
+         * 
+         * Called internally from @ref mainLoopIteration().
+         */
+        bool mainLoopDrawEventIteration();
+
         /**
          * @brief Exit application
          * @param exitCode  The exit code the application should return